U.S. patent number 10,827,660 [Application Number 15/964,665] was granted by the patent office on 2020-11-03 for conductive composition for low frequency emi shielding.
This patent grant is currently assigned to Henkel AG & Co. KGaA, Henkel IP & Holding GmbH. The grantee listed for this patent is Henkel AG & Co. KGaA, Henkel IP & Holding GmbH. Invention is credited to Xiping He, Chenyu Huang, Qili Wu, Lily Yan, Li Yao.
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United States Patent |
10,827,660 |
Huang , et al. |
November 3, 2020 |
Conductive composition for low frequency EMI shielding
Abstract
The present invention relates to a conductive compositions for
low frequency EMI shielding. An EMI shielding composition according
to the present invention comprises a resin comprising a
thermoplastic resin and/or a thermoset resin, a solvent and/or a
reactive diluent and particles, wherein said particles comprise a
mixture of magnetic particles and electrically conductive particles
or magnetic particles coated with electrically conductive material
or a mixture of magnetic particles coated with electrically
conductive material and electrically conductive particles and
wherein, said composition comprises .gtoreq.10% magnetic particles
by weight, by total weight of the composition. The EMI shielding
composition according to the present invention has good electrical
and magnetic conductivity and is suitable as a drop-in solution for
EMI shielding in a wide frequency range, and especially at low
frequency ranges.
Inventors: |
Huang; Chenyu (Shanghai,
CN), Yan; Lily (Shanghai, CN), Wu; Qili
(Shanghai, CN), He; Xiping (Cerritos, CA), Yao;
Li (Irvine, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Henkel IP & Holding GmbH
Henkel AG & Co. KGaA |
Duesseldorf
Duesseldorf |
N/A
N/A |
DE
DE |
|
|
Assignee: |
Henkel IP & Holding GmbH
(Duesseldorf, DE)
Henkel AG & Co. KGaA (Duesseldorf, DE)
|
Family
ID: |
1000005160293 |
Appl.
No.: |
15/964,665 |
Filed: |
April 27, 2018 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20180249603 A1 |
Aug 30, 2018 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCT/CN2015/092954 |
Oct 27, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L
23/552 (20130101); H05K 9/0083 (20130101); H05K
9/0088 (20130101); H01B 1/22 (20130101) |
Current International
Class: |
H01B
1/22 (20060101); H01L 23/552 (20060101); H05K
9/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1887038 |
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Dec 2006 |
|
CN |
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101451057 |
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Jun 2009 |
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CN |
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103773181 |
|
May 2014 |
|
CN |
|
103722832 |
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Dec 2015 |
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CN |
|
0354131 |
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Feb 1990 |
|
EP |
|
785557 |
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Jul 1997 |
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EP |
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H07-183110 |
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Jul 1995 |
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JP |
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H07-183110 |
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Jul 1995 |
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JP |
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2001284877 |
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Oct 2001 |
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JP |
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WO-2015157987 |
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Oct 2015 |
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WO |
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Primary Examiner: Kopec; Mark
Assistant Examiner: Thomas; Jaison P
Attorney, Agent or Firm: Bauman; Steven C.
Claims
The invention claimed is:
1. A cured product of an EMI shielding composition comprising (a) a
resin comprising a thermoplastic resin and/or a thermoset resin;
(b) a solvent and/or a reactive diluent; and (c) particles
comprising magnetic particles coated with an electrically
conductive material or a mixture of electrically conductive
particles and magnetic particles coated with an electrically
conductive material, wherein said composition comprises .gtoreq.10%
magnetic particles by weight of the total composition, wherein said
cured product has a volume resistance less than 5E-02 ohm.cm and
relative magnetic permeability greater than 1.1.
2. A cured product of an EMI shielding composition according to
claim 1, wherein said magnetic particles are selected from the
group consisting of nickel, iron, cobalt, ferrites, permalloy,
iron-nickel alloys, silicon iron (FeSi), FeSiCr alloys, FeSiAl
alloys, FeCO alloys, silver coated nickel, silver coated iron,
silver coated cobalt, silver coated iron-nickel alloys, silver
coated permalloy, silver coated ferrites, silver coated silicone
iron, silver coated FeSiCr alloys, silver coated FeSiAl alloys,
silver coated FeCO alloys and mixtures thereof.
3. A cured product of an EMI shielding composition according to
claim 1, wherein said electrically conductive particles are
selected from the group consisting of silver particles, copper
particles, zinc particles, tin particles, bismuth particles,
antimony particles, indium particles, aluminium particles, gold
particles; graphite particles, carbon particles, silver coated
copper particles, silver coated glass particles, silver coated
aluminium particles, silver coated tin particles, silver coated
bismuth particles, silver coated antimony particles, silver coated
indium particles, silver coated zinc particles, silver coated
graphite, alloy particles made of two or more mixtures from tin,
silver, bismuth, antimony, zinc, copper and indium; silver coated
alloy particles made of two or more metals selected from tin,
silver, bismuth, antimony, zinc, copper and indium; and mixtures
thereof.
4. A cured product of an EMI shielding composition according to
claim 1, wherein said composition comprises magnetic particles from
10 to 95% by weight of total weight of the composition.
5. A cured product of an EMI shielding composition according to
claim 1, wherein said composition comprises electrically conductive
particles from 5 to 85% by weight of total weight of the
composition.
6. A cured product of an EMI shielding composition according to
claim 1, wherein said thermoplastic resin is selected from the
group consisting of phenoxy resin, polyurethane resin, polyester
resin, polyether resin, polysulphone resin, polyvinyl resin,
polyvinylidene resin, polystyrene resin, polystyrene copolymer
resin, fluoro resin, poly(meth)acrylate resin, polyamide resin,
polyimide resin, cellulose resin, polyolefin resin, polycarbonate
resin and mixtures thereof.
7. A cured product of an EMI shielding composition according to
claim 1, wherein said thermoset resin is selected from the group
consisting of allyl resin, vinyl resin, acrylic resin, phenolic
resin, epoxy resin, oxetane resin, isocyanate resin, maleimide
resin, bismaleimide resin, cyanate ester resin, and
silicon-containing resin, cyanoacrylate resin, vinyl ester resin
and mixtures thereof.
8. A cured product of an EMI shielding composition according to
claim 1, wherein said composition comprises from 2 to 60% of said
resin by weight of total weight of the composition.
9. A cured product of an EMI shielding composition according to
claim 1, wherein said solvent is selected from the group consisting
of water, methanol, ethanol, propanol, butanol, ethylene glycol,
propyl acetate, butyl acetate, dibasic ester, ethyl proxitol
ethoxypropanol, carbitol acetate, 2-methoxy-l-methyethyl acetate,
carbitol acetate, 2-methoxy-1-methylethyl acetate, dipropylene
glycol methyl ether, ethylene glycol monobutyl ether acetate,
methyl isobutyl ketone, 2-buthoxy ethanol, diethylene glycol
monobutyl ether acetate, 4-methyl-1,3-dioxolane-2-one, dimethyl
sulfoxide, N-methyl-2-pyroridone, diethylene glycol monobutyl
ether, triethyleneglycol monomethylether, diethyleneglycol ethyl
ether acetate, di ethylene glycol monoethyl ether, diethylene
glycol monomethyl ether, phenol, terpineol, y-butyro lactone, ester
mixture containing methyl succinate and glutaric acid methyl and
dimethyl adipate, butyl glycol acetate and mixtures thereof.
10. A cured product of an EMI shielding composition according to
claim 1, wherein said composition comprises from 5 to 70% of said
solvent by weight of total weight of the composition.
11. A cured product of an EMI shielding composition according to
claim 1, wherein said reactive diluent is selected from the group
consisting of 3,4-epoxycyclohexanecarboxylate, isobornyl acrylate,
2-phenoxyethyl acrylate; neodecanic acid-2,3-epoxypropy ester;
1,4-butanedioldiglycidyl ether; C8-C10 alkyl glycidyl ethers
selected from n-butyglycidyi ether and 2-ethylhexyl glycidyl ether;
aromatic glycidyl ethers selected from phenyl gylcidyl ether,
cresyl glycidyl ether and p-s-butylphenyl glycidyl ether,
tetraglycidylbis-(p-aminophenyl)-methane; styrene oxide and
a-pinene oxide; monoepoxide compounds having other functional
group(s) selected from allyl glycidyl ether, glycidyl methacrylate,
glycidyl acrylate and 1-vinyl-3,4-epoxycyclohexane; a diepoxide
compound selected from (poly) ethylene glycoglycol diglycidyl
ether, (poly) propylene glycol diglyidyl ether, butanediol
diglycidyl ether and neopentyl glycol diglycidyl ether; and a
triepoxide compound selected from trimethylolpropane triglycidyl
ether and glycerin triglycidyl ether; and mixtures thereof.
12. A cured product of an EMI shielding composition according to
claim 1, wherein said composition comprises from 3 to 30% of said
reactive diluent by weight of total weight of the composition.
13. A cured product of an EMI shielding composition according to
claim 1, wherein said composition comprises a curing agent selected
from the group consisting of anhydrides, amine compounds, amide
compounds, imidazole compounds, polyfunctional phenols, carboxylic
acids, thiols, polyols, polyamides, peroxides, hydrogen silicones
and platinum catalysts and mixtures thereof.
14. A cured product of an EMI shielding composition according to
claim 13, wherein said composition comprises from 0.1 to 10% of
said curing agent by weight of the total weight of the
composition.
15. A cured product of an EMI shielding composition according to
claim 1, wherein said electrically conductive particles are silver
particles.
16. A cured product of an EMI shielding composition according to
claim 1, wherein the thermoplastic resin is selected from phenoxy
resin, polyurethane resin, polyester resin, poly(meth)acrylate
resin and mixtures thereof.
17. A cured product of an EMI shielding composition according to
claim 1, wherein the thermoset resin is selected from epoxy resin,
acrylic resin, silicon-containing resin and mixtures thereof.
18. A cured product of an EMI shielding composition according to
claim 1, wherein the reactive diluent is selected from the group
consisting of 3,4-epoxycyclohexanecarboxylate, isobornyl acrylate,
2-phenoxy ethyl acrylate and mixtures thereof.
Description
TECHNICAL FIELD
The present invention relates to a conductive compositions for low
frequency EMI shielding. The composition according to the present
invention has good electrical and magnetic conductivity and is
suitable as a drop-in solution for EMI shielding in a wide
frequency range, and especially at low frequency range.
BACKGROUND OF THE INVENTION
The Electromagnetic Interference (EMI) shielding is required for a
variety of Radio Frequency (RF) electronics components, primarily
used in wireless communication.
The most common EMI shielding solution is using metal lids or cans
to cover target areas or components. However, this solution cannot
meet the increasing need for miniaturization (thinner and thinner
packaging), smaller footprint and higher packing density of
electronic components. Therefore, this solution cannot be used in
some miniature devices due to the metal cap/lid requiring too much
space.
One solution in the industry has been to use conformal shielding
technologies, including plating, sputtering and conductive
adhesive, in order to mimic above-mentioned metal cans.
One way to provide a metal shield is to form it by plating or
sputtering. Sputtering on the package provides a very low UPH (Unit
per hour) process. This is due the fact that the process requires
vacuuming before sputtering and the metal is deposited at atoms
level (takes hours to sputter a layer of several microns thick) and
the devices to be sputtered should be well spaced away from each
other to ensure good coverage at side walls (the number of devices
per sputtering is pretty limited). Plating on the other hand has an
issue on side coverage at strip level and is a complicated process.
Process requires following steps surface pre-treatment, masking
(complicate process, especially for metal lead frame (L/F)),
requires large working space and is a wet process with heavy
pollution.
In addition, industry typically uses electrically conductive metal
fillers including silver, silver coated copper, nickel, gold, etc.
in conductive adhesives (in ink, paste or film forms). Use of these
fillers is providing an adhesive having very low volume
resistivity, close to 1E-05 ohmcm, and making the adhesives perform
well at high frequency >1 GHz EMI shielding and easily obtaining
an EMI shielding effectiveness equal or greater than 30 dB.
However, the drawback of the current adhesive approach is that it
has no EMI shielding effectiveness at relatively low frequency
ranges, in particular in the range from 5 MHz to 200 MHz.
In EMI shielding, primary mechanism for high frequency (GHz or
higher) EMI shielding is reflection, which is primarily determined
by electrical conductivity of shielding layer. While, primary
mechanism for low frequency (MHz or lower) EMI shielding is
adsorption, which is in turn primarily determined by magnetic
permeability of a shielding layer. Therefore, highly electrically
conductive adhesive can be applied on top of susceptible device or
emitting source to block EMI to or from electronics devices in GHz
range. This has been increasingly employed by integrated design and
manufactures (IDMs), design houses and subcontractors on wireless
communication packages, like Wi-Fi modules, 2G/3G/4G cellular
modules, Bluetooth modules etc. Recently, the industry is
progressing towards MHz frequency band to enable new wireless
communication technologies like Near Field Communication (NFC) and
Radio frequency identification (RFID) at 13.56 MHz. For this MHz
level EMI shielding, high electrical conductivity alone cannot
provide adequate shielding effectiveness.
Therefore, there is a need for a conductive composition, which
provide EMI shielding also at low frequency ranges, while
maintaining good EMI shielding at higher frequency ranges, and at
the same time can be applied in miniature devices.
SUMMARY OF THE INVENTION
The present invention relates to an EMI shielding composition
comprising a resin comprising a thermoplastic resin and/or a
thermoset resin, a solvent and/or a reactive diluent and particles
comprising a mixture of magnetic particles and electrically
conductive particles or magnetic particles coated with an
electrically conductive material or a mixture of electrically
conductive particles and magnetic particles coated with an
electrically conductive material, wherein said composition
comprises 10% magnetic particles by weight, by total weight of the
composition.
In addition, the present invention relates to use of a conductive
composition according to the present invention as EMI shielding
material.
Furthermore, the present invention also encompasses a cured product
of an EMI shielding composition according to the present
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an exemplified shape for defining the term "Volume
Resistance".
FIG. 2 shows a graph of response magnetic torque M vs. magnetic
field strength H of an example of the present invention.
FIG. 3 schematically shows a shielding effect of a shield material
of an example of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
In the following passages the present invention is described in
more detail. Each aspect so described may be combined with any
other aspect or aspects unless clearly indicated to the contrary.
In particular, any feature indicated as being preferred or
advantageous may be combined with any other feature or features
indicated as being preferred or advantageous.
In the context of the present invention, the terms used are to be
construed in accordance with the following definitions, unless a
context dictates otherwise.
As used herein, the singular forms "a", "an" and "the" include both
singular and plural referents unless the context clearly dictates
otherwise.
The terms "comprising", "comprises" and "comprised of" as used
herein are synonymous with "including", "includes" or "containing",
"contains", and are inclusive or open-ended and do not exclude
additional, non-recited members, elements or method steps.
The recitation of numerical end points includes all numbers and
fractions subsumed within the respective ranges, as well as the
recited end points.
When an amount, a concentration or other values or parameters
is/are expressed in form of a range, a preferable range, or a
preferable upper limit value and a preferable lower limit value, it
should be understood as that any ranges obtained by combining any
upper limit or preferable value with any lower limit or preferable
value are specifically disclosed, without considering whether the
obtained ranges are clearly mentioned in the context.
Unless otherwise defined, all terms used in the disclosing the
invention, including technical and scientific terms, have the
meaning as commonly understood by one of the ordinary skill in the
art to which this invention belongs to. By means of further
guidance, term definitions are included to better appreciate the
teaching of the present invention.
The present invention provides an EMI shielding composition
comprising a resin comprising a thermoplastic resin and/or a
thermoset resin, a solvent and/or a reactive diluent and particles
comprising a mixture of magnetic particles and electrically
conductive particles or magnetic particles coated with an
electrically conductive material or a mixture of electrically
conductive particles and magnetic particles coated with an
electrically conductive material, wherein said composition
comprises .gtoreq.10% magnetic particles by weight, by total weight
of the composition.
The applicant has found out that by incorporating both magnetic
fillers and electrically conductive fillers into an adhesive
composition, providing magnetic permeability and high electrical
conductivity lead to a desired EMI shielding effectiveness at both
high and low frequency ranges.
Each of the essential components of the EMI shielding composition
according to the present invention are described in details
below.
An EMI shielding composition according to the present invention
comprises a resin comprising a thermoplastic resin or a thermoset
resin or a mixture of a thermoplastic resin and a thermoset
resin.
Thermoplastic Resin
An EMI shielding composition according to the present invention
comprises a thermoplastic resin. A wide variety of known
thermoplastic resins can be used in the present invention. The
thermoplastic resin may be any thermoplastic resin.
Suitable thermoplastic resins for use in the present invention are
selected from the group consisting of phenoxy resin, polyurethane
resin, polyester resin, polyether resin, polysulphone resin,
polyvinyl resin, polyvinylidene resin, polystyrene resin,
polystyrene copolymer resin, fluoro resin, poly(meth)acrylate
resin, polyamide resin, polyimide resin, cellulose resin,
polyolefin resin, polycarbonate resin and mixtures thereof.
Preferably, thermoplastic resin is selected from the group
consisting phenoxy resin, polyurethane resin, polyester resin,
poly(meth)acrylate resin and mixtures thereof.
More preferably said thermoplastic resin is selected from the group
consisting of poly methyl methacrylate resin, co-polymer of
bisphenol A and epichlorohydrin, saturated polyester resin,
unsaturated polyester resin, saturated polyether resin, unsaturated
polyether resin, aromatic polyurethane resin,
polytetrafluoroethylene resin, co-polymer of styrene and butadiene,
polyvinylidene fluoride resin, polyvinylchloride resin and mixtures
thereof.
Suitable thermoplastic resins to be used in the present invention
have a molecular weight Mw greater than 10000, preferably having
M.sub.w (average) from 30000 to 60000 and M.sub.n (average) from
10000 to 20000. Molecular weight is determined by using gel
permeation chromatography (GPC).
Suitable commercially available thermoplastic resins for use in the
present invention are for example phenoxy resins, from InChemRez,
Estane TPU from Lubrizol, Epicon from DIC and Vitel polyesters from
Bostik.
Thermoset Resin
An EMI shielding composition according to the present invention
comprises a thermoset resin. A wide variety of known thermoset
resins can be used in the present invention.
Exemplary suitable thermoset resins to be used herein the present
invention include allyl resin, vinyl resin, acrylic resin, phenolic
resin, epoxy resin, oxetane resin, isocyanate resin, maleimide
resin, bismaleimide resin, cyanate ester resin, and
silicon-containing resin, cyanoacrylate resin, vinyl ester resin
and mixtures thereof, preferably, thermoset resin is selected from
epoxy resin, acrylic resin, silicon-containing resin and mixtures
thereof.
Preferably, thermoset resin is selected from the group consisting
of polyurethane acrylate, polyacrylate, epichlorohydrin-phenol
formaldehyde resin, liquid bis-maleimide resin, N-phenyl maleimide
resin, organo-silicone resin, polymethyl silicone resin, polyethyl
silicone resin, polyaryl silicone resin, polyalkylaryl silicone
resin, bisphenol epoxy resin, biphenyl epoxy resin, siloxane epoxy
resin, toluene diisocyanate resin, methylenediphenyl diisocyanate
resin and mixtures thereof.
Suitable thermoset resin may be a multifunctional resin with a
mixture of functional groups such as epoxide resins having other
functional group(s) selected from allyl glycidyl ether, glycidyl
methacrylate, glycidyl acrylate and
1-vinyl-3,4-epoxycyclohexane.
Suitable commercially available thermoset resins for use in the
present invention are for example Epiclon N-730 from DIC, UN9200A
from Sartomer, CM 1003 from Henkel, VQM 803 from Evonik.
Suitable thermoset resin for use in the present invention have a
molecular weight Mw greater than 1000. Molecular weight is
determined by using gel permeation chromatography (GPC).
An EMI shielding composition according to the present invention
comprises a resin from 2 to 60% by weight of total weight of the
composition, preferably from 4 to 45% and more preferably from 4 to
30% and most preferably from 4 to 20%.
It is preferred that the total amount of the thermoplastic resin
and thermoset resin in the EMI shielding composition does not
exceed 60% by weight of total weight of the composition. Too high
resin quantity in the composition leads to a poor electrical
conductivity and magnetic permeability, and as a result, poor EMI
shielding properties. On the other hand, if the total amount of
resin is less than 2% by weight of total weight of the composition,
the adhesion properties may be negatively affected.
An EMI shielding composition according to the present invention
comprises particles. In one embodiment particles comprise a mixture
of magnetic particles and electrically conductive particles. In
another embodiment particles comprise a magnetic particles coated
with an electrically conductive material. Yet in another
embodiment, particles comprise a mixture of electrically conductive
particles and magnetic particles coated with an electrically
conductive material.
Magnetic Particles
An EMI shielding composition according to the present invention
comprises magnetic particles. Suitable magnetic particles are for
example ferromagnetic particles and nanocrystalline ferromagnetic
particles.
More specifically, suitable magnetic particles for use in the
present invention are selected from the group consisting of nickel,
iron, cobalt, ferrites, iron-nickel alloys, permalloy, silicon iron
(FeSi), FeSiCr alloys, FeSiAl alloys, FeCo alloys and mixtures
thereof.
Suitable magnetic particles coated with an electrically conductive
material for use in the present invention are selected from the
group consisting of silver coated nickel, silver coated iron,
silver coated cobalt, silver coated iron-nickel alloys, silver
coated permalloy, silver coated ferrites, silver coated silicon
iron, silver coated FeSiCr alloys, silver coated FeSiAl alloys,
silver coated FeCO alloys and mixtures thereof.
Preferably magnetic particles are selected from the group
consisting of ferrites, iron-nickel alloys, iron, nickel, FeSiAl
alloys, FeSiCr alloys, silver coated nickel, silver coated iron,
silver coated iron-nickel alloys and mixtures thereof.
Suitable commercially available magnetic particles for use in the
present invention are for example Nickel type 255 from INCO, silver
coated nickel AO-QCS-78 from DOWA and FeNi alloys, FeSiAl from
Carpenter Powder Products and Ferrites from PPTechnologies.
Magnetic particles, can be in a powder form or in a flake form or
mixture of these two. Preferably, magnetic particles are a mixture
of particles in powder form and in flake form. Suitable magnetic
particles used in the present invention have a particle size
preferably greater than 10 nm and they have a mean average particle
size less than 75 .mu.m, preferably less than 50 .mu.m.
In general, too big particle size leads to uneven surface of the
EMI shielding layer and there also may be some small voids or holes
in the EMI shielding layer, and therefore, EMI shielding coverage
is not full. Whereas, too small particle size leads potential risk
of low conductivity and poor formulation rheology.
An EMI shielding composition according to the present invention
comprises 10% magnetic particles by weight, by total weight of the
composition. Equal or greater quantity than 10% is required to
provide adequate magnetic properties in order to provide an EMI
shielding at low frequency ranges.
An EMI shielding composition according to the present invention
comprises magnetic particles from 10 to 95% by weight of total
weight of the composition, preferably from 20 to 90%, more
preferably from 30 to 85% and more preferably from 40 to 85%.
If the quantity of magnetic particles exceeds 95%, the composition
does not provide adequate adhesion. On the other hand, quantity
below 10% does not to provide adequate magnetic properties in order
to provide an EMI shielding at low frequency ranges.
Electrically Conductive Particles
An EMI shielding composition according to the present invention
comprises electrically conductive particles. Suitable electrically
conductive particles for use in the present invention are selected
from the group consisting of silver particles, copper particles,
zinc particles, tin particles, bismuth particles, antimony
particles, indium particles, aluminium particles; gold particles,
graphite particles, carbon particles, silver coated copper
particles, silver coated glass particles, silver coated aluminium
particles, silver coated tin particles, silver coated bismuth
particles, silver coated antimony particles, silver coated indium
particles, silver coated zinc particles, silver coated graphite,
alloy particles made of two or more mixtures from tin, silver,
bismuth, antimony, zinc, copper and indium; silver coated alloy
particles made of two or more metals selected from tin, silver,
bismuth, antimony, zinc, copper and indium; and mixtures thereof,
preferably, the electrically conductive particles are silver
particles.
Suitable commercially available electrically conductive particles
for use in the present invention are low tap density (tap density
in the range of 0.1 to 3.5 g/cm.sup.3) silver powders and flakes
from Metalor or other Silver particle manufactures such as Ames
Goldsmith.
Electrically conductive particles, can be in a powder form or in a
flake form or mixture of these two. Preferably, electrically
conductive particles are a mixture of particles in powder form and
in flake form.
Suitable electrically conductive particles used in the present
invention have a particle size preferably greater than 10 nm and
they have a mean average particle size less than 75 .mu.m,
preferably less than 50 .mu.m.
In general, too big particle size leads to uneven surface of the
EMI shielding layer and there also may be some small voids or holes
in the EMI shielding layer, and therefore, EMI shielding coverage
is not full. Whereas, too small particle size leads potential risk
of low conductivity and high viscosity.
An EMI shielding composition according to present invention
comprises electrically conductive particles from 5 to 85% by weight
of total weight of the composition, preferably from 10 to 80%, and
more preferably from 10 to 73%.
If the quantity of electrically conductive particles exceeds 85%,
the composition does not provide adequate adhesion, and in addition
it is difficult to form a film from the composition. On the other
hand if the quantity is below 5%, the composition does not have
adequate conductivity.
An EMI shielding composition according to the present invention
comprises a solvent or reactive diluent or mixture of a solvent and
a reactive diluent.
Solvent
An EMI shielding composition according to the present invention
comprises a solvent. A solvent is particularly preferred when a
thermoplastic resin is used.
Suitable solvents for use in the present invention are selected
from the group consisting of water, methanol, ethanol, propanol,
butanol, ethylene glycol, propyl acetate, butyl acetate, dibasic
ester, ethyl proxitol ethoxypropanol, carbitol acetate,
2-methoxy-1-methyethyl acetate, carbitol acetate,
2-methoxy-1-methylethyl acetate, dipropylene glycol methyl ether,
ethylene glycol monobutyl ether acetate, methyl isobutyl ketone,
2-buthoxy ethanol, diethylene glycol monobutyl ether acetate,
4-methyl-1,3-dioxolane-2-one, dimethyl sulfoxide,
N-methyl-2-pyroridone, diethylene glycol monobutyl ether,
triethyleneglycol monomethylether, diethyleneglycol ethyl ether
acetate, diethylene glycol monoethyl ether, diethylene glycol
monomethyl ether, phenol, terpineol, .gamma.-butyro lactone, ester
mixture containing methyl succinate and glutaric acid methyl and
dimethyl adipate, butyl glycol acetate and mixtures thereof.
Preferably said solvent is selected from the group consisting of
2-methoxy-1-methyethyl acetate, butyl glycol acetate, carbitol
acetate, dibasic ester and mixtures thereof.
Suitable commercially available solvents for use in the present
invention are for example 2-methoxy-1-methyl ethyl acetate and
dibasic ester from Sigma Aldrich; and butyl glycol acetate and
carbitol acetate from EASTMAN.
An EMI shielding composition according to the present invention
comprises a solvent from 5 to 70% by weight of total weight of the
composition, preferably from 15 to 50%, more preferably from 15 to
45%.
It is preferred that the total quantity of the solvent in the EMI
shielding composition according to the present invention does not
exceed 70% by weight of total weight of the composition. High
solvent quantity in the composition leads to a poor electrical
conductivity, poor magnetic properties and poor adhesion. In
addition, too high solvent quantity leads low dry film thickness
and that will cause poor shielding performance. On the other hand,
low solvent quantity leads to high viscosity and poor electrical
conductivity and poor magnetic properties.
Reactive Diluent
An EMI shielding composition according to the present invention
comprises a reactive diluent. Reactive diluent is particularly
preferred when thermoset resins are used as a resin. Suitable
reactive diluents for use in the present invention are selected
from the group consisting of 3,4-epoxycyclohexanecarboxylate,
isobornyl acrylate, 2-phenoxyethyl acrylate; neodecanic
acid-2,3-epoxypropyl ester; 1,4-butanedioldiglycidyl ether; C8-C10
alkyl glycidyl ethers selected from n-butylglycidyl ether and
2-ethylhexyl glycidyl ether; aromatic glycidyl ethers selected from
phenyl gylcidyl ether, cresyl glycidyl ether and p-s-butylphenyl
glycidyl ether, tetraglycidylbis-(p-aminophenyl)-methane; styrene
oxide and .alpha.-pinene oxide; monoepoxide compounds having other
functional group(s) selected from allyl glycidyl ether, glycidyl
methacrylate, glycidyl acrylate and 1-vinyl-3,4-epoxycyclohexane; a
diepoxide compound selected from (poly)ethylene glycol diglycidyl
ether, (poly)propylene glycol diglycidyl ether, butanediol
diglycidyl ether and neopentyl glycol diglycidyl ether; and a
triepoxide compound selected from trimethylolpropane triglycidyl
ether and glycerin triglycidyl ether; and mixtures thereof,
preferably reactive diluent is selected from the group consisting
of 3,4-epoxycyclohexanecarboxylate, isobornyl acrylate, 2-phenoxy
ethyl acrylate and mixtures thereof.
Suitable commercially available reactive diluents for use in the
present invention are for example RE1825 from DAICEL and Isobornyl
acrylate such as SR506 from Sartomer.
An EMI shielding composition according to the present invention
comprises a reactive diluent from 3 to 30% by weight of total
weight of the composition, preferably from 5 to 20%, more
preferably from 5 to 15%.
It is preferred that the total quantity of the reactive diluent in
the EMI shielding composition according to the present invention
does not exceed 30% by weight of total weight of the composition.
Too high reactive diluent quantity in the composition leads to a
poor electrical conductivity, poor magnetic properties and poor
adhesion. On the other hand low reactive diluent quantity leads to
high viscosity and poor electrical conductivity and poor magnetic
properties.
Curing Agent
An EMI shielding composition according to the present invention may
further comprise a curing agent. A curing agent is especially
preferred when EMI shielding composition comprises a thermoset
resin.
Suitable curing agents to be used herein the present invention
include anhydride-containing compounds; nitrogen-containing
compounds such as amine compounds, amide compounds and imidazole
compounds; polyfunctional phenols; carboxylic acids; thiols;
polyols; polyamides; peroxides; hydrogen silicones; and platinum
catalysts and mixtures thereof. More particularly, the composition
may be cured using stoichiometric amounts of a curing agent, such
as anhydrides, primary and secondary amines, polyfunctional
phenols, carboxylic acids, thiols and polyols; the composition may
be cured using non-stoichiometric amounts of catalysts, such as
tertiary amines, imidazoles and peroxides; or the composition may
be cured through a combination of such curing agents and
catalysts.
Preferably said curing agent is selected from the group consisting
of 1-cyanoethyl-2-ethyl-4-methylimidazole, blocked amines, modified
imidazoles, dodecenyl succinic anhydride, peroxides and mixtures
thereof.
Suitable commercially available curing agents for use in the
present invention are for example Imicure HAPI from Airproducts,
EMI-24-CN from PCI Synthesis, EH 2021 from Adeka and DiCup from
AkzoNobel.
An EMI shielding composition according to the present invention may
comprise a curing agent from 0.1 to 20% by weight of the total
weight of the composition, preferably from 0.2 to 10%, more
preferably from 0.5 to 5%, and even more preferably from 0.75 to
2.5%.
Cross-Linking Agent
An EMI shielding composition according to the present invention may
further comprise a cross-linking agent. A cross linking agent is
particularly preferred when said EMI shielding composition
comprises a silicone based resin. Suitable cross linking agents for
use in the present invention include silicones hydrogen-containing
silicones, saline coupling agents, silicic acid, platinum catalyst
and mixtures thereof.
Suitable commercially available cross-linking agents for use in the
present invention are for example Silopren U cross linking agent
430 from Momentive.
An EMI shielding composition according to the present invention may
comprise a cross linking agent from 0.01 to 10% by weight of total
weight of the composition, preferably from 0.5 to 5% and more
preferably from 1.5 to 3% and most preferably from 1.75 to
2.75%.
Photoinitiator
An EMI shielding composition according to the present invention may
further comprise a photoinitiator. A photoinitiator is particularly
preferred, when the EMI shielding composition comprises silicone
resin.
Suitable photoinitiators to be used herein the present invention
are for example hydroxyketones, aminoketones,
monoacylphosphinoxides, bisacylphosphinoxides, antimoniates,
organic peroxides, azo-initiators and mixtures thereof. More
particularly a photoinitiator may be
bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide.
Suitable commercially available photoinitiators for use in the
present invention are for example Irgacure 819 from BASF.
An EMI shielding composition according to the present invention may
comprise a photoinitiator from 0.01 to 2.5% by weight of total
weight of the composition, preferably from 0.1 to 2% and more
preferably from 0.2 to 2%.
Adhesion Promoter
An EMI shielding composition according to the present invention may
further comprise an adhesion promoter. Suitable adhesion promoters
to be used herein the present invention include silanes.
Preferably adhesion promoter is selected from the group consisting
of (3-glycidyloxypropyl)-trimethoxysilane,
.gamma.-methacryloxypropyltrimethoxysilane,
bis[3-(triethoxysilyl)-propyl]-tetrasulfide and mixtures
thereof.
Suitable commercially available adhesion promoters for use in the
present invention are for example Z6040 and Z6030 from Dow Corning;
and TS4 from UCT United chemical Technologies.
An EMI shielding composition according to the present invention may
comprise an adhesion promoter from 0.05 to 2% by weight of the
total weight of the composition, preferably from 0.1 to 1%.
Rheology Modifier
An EMI shielding composition according to the present invention may
further comprise a rheology modifier. Suitable rheology modifiers
to be used herein the present invention include silicones and
siloxanes such as dimethyl silicone polymer with silica and fumed
silica.
Suitable commercially available rheology modifiers for use in the
present invention is for example Cab-O-Sil TS-720 from Cabot
Corporation.
An EMI shielding composition according to the present invention may
comprise a rheology modifier from 0.01 to 10% by weight of total
weight of the composition, preferably from 0.5 to 5% and more
preferably from 1.5 to 3% and most preferably from 1.75 to
2.75%.
Wetting and Dispersing Agent
An EMI shielding composition according to the present invention may
further comprise a wetting and dispersing agent. A wetting and
dispersing agent is used to reduce viscosity of the composition and
to improve filler dispersity.
Suitable wetting and dispersing agents for use in the present
invention are for example acidic polyesters and hydroxy-functional
alkylammonium salt of an acidic copolymer.
Suitable commercially available wetting and dispersing agents for
use in the present invention are for example BYK-W985 and BYK W-969
from Altana.
An EMI shielding composition according to the present invention may
comprise wetting and dispersing agent from 0.01 to 5% by weight of
total weight of the composition, preferably from 0.1 to 3% and more
preferably from 0.2 to 2%.
In addition, the EMI shielding composition according to the present
invention may further comprise optional ingredients such as surface
gloss promoter, conductivity promoter, anti-bleeding agent and
corrosion inhibitor.
The EMI shielding composition according to the present invention
may be in a form of a paste, a liquid or a film.
The Emi shielding composition according to the present invention is
suitable as a drop-in solution for EMI shielding in a wide
frequency range from 1 MHz to 5 GHz, providing especially effective
EMI shielding at relatively low frequency range from 5 MHz to 200
MHz.
An EMI shielding composition according to the present invention can
be used as an EMI shielding material in electrical devices. EMI
shielding composition according to the present invention can be
used for EMI shielding for example in semiconductor package like
SIP, radio frequency device, embedded multimedia device or board
level package that can replace current metal cap/lid. These
packages can be used for example in mobile devices, wearables,
computers, cars and medical instruments.
The present invention uses the EMI shielding composition on top of
and/or inside the package. The EMI shielding composition according
to the present invention can be applied for example by spray
coating, by dispensing or jetting or printing. The spray coating
can be air spray coating and electrostatic spray coating. The EMI
shielding composition according to the present invention has
slightly different physical properties depending on the application
method.
Spray coating type EMI shielding composition according to the
present invention has a viscosity at 5 rpm from 100 to 30000 cps,
preferably from 300 to 5000 cps, more preferably from 500 to 3250
cps, wherein viscosity is measured according to method described
below.
Viscosity is measured by using standard testing method for
Brookfield HBDV-III ULTRA with CPE-51 for Electronic Gap Setting
Model, therefore, viscosity is measured by using Brookfield
HBDV-III ULTRA with CPE-51 for Electronic Gap Setting Model.
Testing temperature is set at 25.degree. C..+-.0.1.degree. C. and
kept constant. Testing data is measured at 0.5 rpm and 5 rpm
separately.
Thixotrophy index (TI) value is calculated from the ratio of data
at 0.5 rpm by that at 5 rpm (viscosity at 0.5 rpm/viscosity at 5
rpm).
Spray coating type EMI shielding composition according to the
present invention has a thixotropic index greater than 1,
preferably from 2 to 8.
Spray coating type EMI shielding composition according to the
present invention has a yield stress greater than 1, preferably
from 2.5 to 8, wherein yield stress is measured according to test
method disclosed below
Yield stress is measured by using standard testing method for
Rheometer AR2000, and therefore, yield stress is measured by using
Rheometer AR 2000, from TA Instruments. Casson mode is used to
calculate the yield stress.
Dispensing/jetting coating type EMI shielding according to the
present invention has a viscosity at 5 rpm from 100 to 300000 cps,
preferably from 1000 to 30000 cps, more preferably from 3000 to
15000 cps, wherein viscosity is measured according to test method
described above.
Dispensing/jetting coating type EMI shielding composition according
to the present invention has a thixotropic index (viscosity at 0.5
rpm/viscosity at 5 rpm) greater than 0, but less than 5, preferably
less than 2.5.
Dispensing/jetting coating type EMI shielding composition according
to the present invention has a yield stress is greater than 0, but
less than 30, preferably less than 10, wherein yield stress is
measured according to method described above.
The present invention is also directed to a cured product of an EMI
shielding composition according to the present invention.
EMI shielding composition according to the present invention
provides considerable electrical and magnetic conductivity after
full cure. Preferably volume resistivity of the cured EMI shielding
composition according to the present invention is <5E-02 ohmcm.
Preferably relative magnetic permeability of the cured EMI
shielding composition according to the present invention is greater
than 1.1. The test methods for volume resistivity and relative
magnetic permeability are described in detail in the examples
section below.
EMI shielding composition according to the present invention
provides shielding effectiveness equal or greater than 20 dB,
preferably equal or greater than 30 and more preferably equal or
greater than 40 dB, wherein the shielding effectiveness is measured
according to test method described in the experimental section
below.
EXAMPLES
Volume Resistance
FIG. 1 shows an exemplified shape for defining the term "Volume
Resistance".
for: R=.rho.L/S [.OMEGA., ohm]
.rho.: at 25.degree. C. the (volume) resistivity of conductor with
1 m length and 1 mm.sup.2 cross section area
Volume Resistance: .rho.=RS/L [.mu..OMEGA.m, .mu.ohmm, 10E-4
ohm-cm]
Agilent 34401A digital multimeter, Gen Rad 1689 Precision RLC
Digibridge was used in the measurements.
A special four-point probe test fixture was made from an acrylic
material with four spring-loaded contacts. The contacts were set
into the acrylic in order that the current contacts were two inches
(5.08 cm) apart, the voltage contacts were between the two current
contacts, and the voltage contacts were separated from each current
contact by 0.5 inch (1.27 cm).
Sample Preparation:
Two rolls of 3M Magic Scotch Tape were loaded into the jig, 0.1''
(0.254 cm) apart.
A cleaned glass slide having two parallel strips of Scotch tape
that were 0.1'' (0.254 cm) apart was slid along the flat bar of the
jig. No wrinkles or bubbles were trapped in the tape. NOTE: The
glass plate was cleaned with alcohol or acetone and air dried
before the use.
The taped glass plate was placed onto a sheet of laboratory paper
towel (taped side facing up) and a dab of the adhesive was dropped
onto the glass plate between the two tape strips.
The straight edge of another glass plate (or a single edge razor
blade) was used to squeeze the adhesive between the two strips of
the tape from one end of the glass slide to the other end (glass
plate was maintained in about a 30.degree. angle between the
surface of the glass plate and the straight edge,). The adhesive
was firmly squeezed, but not an excessive force was not used. The
length of the applied strip was at least 2.5 in (6.35 cm).
The two strips of the tape were removed from the glass slide and
the sample was cured in a preheated oven according to the specified
cure schedule.
The specimens were removed from the oven (or hot plate) and cooled
to the room temperature and measured.
Relative Magnetic Permeability
Sample Preparation:
A pressurized mould (2 mm*2 mm*0.3 mm thickness) was sprayed with
some release agent. A flat, cylindrical specimen was prepared by
squeezing or pouring the adhesive paste into the mould. The
specimen was cured in a preheated oven (under pressure to eliminate
voids) according to the specified cure schedule provided. Note: It
may be necessary to cure the specimen for an extended 1 hour. The
additional 1 hour would allow the mould enough time to be heated up
to the specified temperature. This would ensure the specimen is
fully cured.
Test Equipment: PPMS (Physical Property Measurement System) from
Quantum Design. Sample size: 2.5 mm*2.5 mm*0.3 mm. Input: magnetic
field strength H. Response magnetic torque M. Output: After a
linear fitting (before saturation) the slope is the
permeability.
FIG. 2 shows a graph of response magnetic torque M vs. magnetic
field strength H of an example of the present invention. The
applied magnetic field H varied from 0 Oe to 30000 Oe with a rate
100 Oe/s, but the M reached saturation value for most samples after
10000 Oe, which means the linear part was from 0 Oe to 10000
Oe.
The Shielding Effectiveness
The film having a thickness from 3 to 150 .mu.m is prepared from
the composition according to the present invention. The thickness
of the film varies depending on application, but is simulating the
actual thickness in the target application.
FIG. 3 schematically shows a shielding effect of a shield material
of an example of the present invention. The shielding effect is
done through placing the shield material between EMI wave source
and EMI wave detector. The shielding effectiveness is defined as
the log of the ratio of transmitted EM wave and incident EM
wave.
Shielding effectiveness is calculated from the following equation:
SE (dB)=10.times.log(Ei/Et), in which Ei stands for incident energy
and Et stands for transmitted energy. The factor in the equation
may be 10 or 20 depending if the ratio is energy or voltage, if the
energy of the EM wave is measured, then factor 20 is used and on
the other hand, the voltage used to generate the EM wave is
measured, then the factor is 10.
The following examples were prepared by following method:
All materials except particles were added into one container. The
mixture were mixed by hand and followed by 3 roll mill in order to
mix well the particles into the resin system. Magnetic and
electrically conductive particle were added into the mixture and
hand mixed and followed by mixing by Thinky mixer (with revolution
and rotation mix) by 1000 rpm for 1 min with degassing.
TABLE-US-00001 TABLE 1 Comparative example Comparative example
Ingredient Epoxy Resin Epiclon 830S from DIC 7 Epoxy Resin RE1825
from DAICEL 10 Curing Agent HAPI from Airproduct 1 Silver C-2462P
from Metalor 16 Silver coated copper AgCu0204 from 66 Ames Advanced
Materials corporation 100 Properties Volume Resistance (ohm cm) 6 *
10-5 Relative Magnetic permeability 0.99
TABLE-US-00002 TABLE 2 Ingredient Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex.
6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Epoxy Resin Epiclon 830S from DIC
7 1 7 7 7 7 7 7 7 Epoxy Resin RE1825 from DAICEL 10 10 10 10 10 10
10 10 10 reactive diluent Acrylate SR506 from Sartomer reactive 5
diluent BMI resin from Henkel 10 Silicone resin VQM803 from Evonik
6.5 Silicone resin VQM885 from Evonik 6.5 Curing Agent HAPI from
Air product 1 1 1 1 1 1 1 1 1 0.5 Hydogene silicone Silopren U 2
crosslinking agent 430 from Momentive Photoinitiator Irgacure 819
from BASF 0.5 Silver C-2462P from Metalor 72 62 52 41 41 30 30 20
32 54.5 54.5 Nickel Type 255 from INCO 10 20 30 41 30 30 Silver
coated nickel AO-QCS-78 from 41 52 DOWA Silver coated iron 6672-2
from Technic 52 62 Silver coated Fe--Ni alloy P733-2 from 50
Metalor Ingredient Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Ex. 18
Phenoxy Resin from 4.5 4.5 4.5 4.5 4.5 4.5 InChemRez Estane PU
resin 4.5 Solvent 2-methoxy-1-methyethyl 16.67 16.67 16.67 16.67
16.67 16.7 18 acetate from Sigma Aldrich magnetic filler Permalloy
70.5 62.16 magnetic filler Ferrite 70.5 magnetic filler Iron 70.5
FeSiAl 70.5 68.8 FeSiCr 70.5 silver Filler KP-84 from Ames 8.33
8.33 8.33 16.67 8.33 8.33 8.2 Goldsmith
TABLE-US-00003 TABLE 3 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7
Ex. 8 Ex. 9 Volume 3*10-5 3*10-5 1*10-4 2*10-3 2*10-3 1*10-2 6*10-4
9*10-3 1*10-4 resistance (ohm cm) Relative 1.15 1.24 1.41 1.51 1.61
1.69 magnetic permeability Shielding 10 20 effectiveness dB
10-50M
TABLE-US-00004 TABLE 4 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15
Ex. 16 Ex. 17 Ex. 18 Volume 1*10-3 6*10-3 3*10-3 6*10-3 3*10-3
5*10-4 5* 10-3 6*10-3 9*10-3 resistance (ohm com) Relative 1.4 1.35
8.5 9.7 7.5 10 7.8 9.7 magnetic permeability Shielding 48 62
effectiveness dB 10-50M
The examples according to the present invention exemplify that
magnetic particle type and loading have an effect on relative
magnetic permeability, whereas the resin system do not impact a lot
on relative magnetic permeability. Ni--Fe Alloy provides highest
relative magnetic permeability followed by iron and nickel. Higher
silver particle loading provides the electrical conductivity.
Furthermore, higher the magnetic loading, higher magnetic
permeability. It is preferred to have magnetic filler loading
between 60-70% in order to achieve magnetic permeability greater or
equal than 4.
* * * * *